The present invention relates to heat exchangers and fan coils of the type used in refrigeration and air conditioning systems, and is directed more particularly to a heat exchanger slab assembly that has improved condensate retention properties.
All refrigeration and air conditioning systems intake relatively warm air that has an unknown moisture content and discharges air at a reduced temperature. In the process, intake air is passed over fan coils or other heat exchangers which carry refrigerant liquids, such as ammonia or water, which have a temperature lower than that of the intake air. As this occurs, the moisture in the air condenses on the fins of the fan coils or heat exchangers, and forms droplets of water that eventually become large enough to flow under the force of gravity. This condensate water then flows along the surface of the fins until it reaches a pan or tube from or through which it can be drained off.
An important consideration in the handling of condensate is the need to prevent it from being blown off of the fins and entrained in the air flowing out of the heat exchanger or fan coil. This is because such entrained moisture flows through the duct system of the space to be cooled, where it can cause moisture damage, rot and mildew. The problem of preventing condensate from flowing off of the fins of heat exchangers and fan coils is complicated by the fact that, in order to provide the maximum possible surface area for heat exchange, heat exchangers and fan coils are often made up of two or more generally planar heat exchanger subassemblies, commonly referred to as slabs, which have their planes oriented obliquely with respect to the direction of air flow and which, together, occupy the height and width of the duct within which they are located. In one configuration, known as an "A coil", two slabs are formed into an A or V shaped slab assembly the apex of which points either upstream into or downstream from the air flow. In another configuration, known as an "N coil" three slabs are formed into and N or Z shaped slab assembly having a first apex that points upstream and a second apex which points downstream.
The retention of condensate in multi-slab slab assemblies is relatively straightforward in heat exchangers in which the slabs are mounted vertically with one slab behind another, i.e. in fluidic series with one another with respect to the air flow through the duct. This is because, in such slab assemblies, condensate that flows down the fins of such slabs under the force of gravity remains in parallel streams which do not cross from slab to slab and which empty into a common catchment tray and from there directed into a drain for disposal. The problem with this vertical orientation is that the downstream ones of the slabs are in the thermal shadow of the upstream slabs and therefore exchange heat less efficiently.
In the case of multi-slab heat exchangers in which the slabs are mounted horizontally with one slab above or below another, i.e., in parallel relationship with respect to the air flow through the duct, the processing of condensate is more difficult. This is because condensate flowing along the fins of such slab assemblies under the force of gravity flows in streams that must cross from one slab to another before reaching their catchment tray, and because condensate is more easily blown off of the slabs as it crosses from one slab to another, i.e., when it is in proximity to the apexes of such slab assemblies.
Prior to the present invention, the problem of retaining condensate within horizontally oriented slab assemblies was dealt with in one of two ways. One of these was to include splitter plates between adjacent slabs. These splitters served to intercept and collect condensate that was blown off of the overlying slabs at the apexes of the slab assembly and direct it downwardly onto the underlying slab thereof. The problem with this solution is that condensate flowing along the surface of the splitter moves toward the edges of the underlying slab, where it is directed into a relatively small number of the fins thereof. Once there, it causes the condensate carrying capacity of these outer fins to be exceeded, thereby allowing condensate to blow off of the slab assembly and become entrained in the air flow leaving the heat exchanger.
Another solution to the problem preventing condensate blow off included the provision, for each overlying slab, of a separate, direct drainage path to the common catchment tray. This solution had the advantage that it eliminated the need for slab-to-slab flow of condensate, but it made the slab assembly and the heat exchanger of which it was a part considerably more complex and expensive. This complexity and expense is compounded by the fact that, for safety reasons, all drainage paths must be provided with a parallel, redundant drainage path that protects the building in which it is used from being flooded as a result of the blockage of any single drainage path.
Thus, prior to the present invention, there has existed a need for a condensate retaining apparatus which is effective, but which also is both simple and inexpensive.